This study investigates the effects of torrefaction temperature and time on the energy content and storage stability of bio-char derived from corn stover feedstock. The batch torrefaction system in this study uses 91.4 cm × 25.4 cm diameter reactors with electrical heating elements to torrefy large samples of corn stover. The reactor is typically loaded with 0.5 kg samples of chopped corn stover (stalks, leaves, and cobs) with particle surface areas ranging from 0.5–2.4 cm2. The operating temperatures range from 230–340 degrees C, while the operating times range from 30–60 minutes. After each reaction trial, the energy content of the bio-char is quantified using the heat of combustion value obtained from bomb calorimeter tests on each of the samples. Values from these tests are compared to previous research to investigate the feasibility of larger-scale torrefaction reactions with mixed component stover. Temperature and time profiles are obtained from an Arduino output to investigate temperature behaviors during the reaction. The temperature and energy content can provide the basis for defining the phases of torrefaction.
The long-term goal of this research is to assess the viability of producing a high energy, storable bio-char as well as a usable biogas from the torrefaction process of corn stover feedstocks. Since compounds within the corn stover have different reaction rates, a composition analysis of samples at various stages in torrefaction will indirectly provide information on the usability of the biogas and behaviors of organic compounds in the reaction. Therefore, the torrefaction conditions must be specified before moving forward.